1. Field of the Invention
The present invention relates to an electron beam exposure mask used for transferring a fine pattern in a semiconductor device manufacturing process and the like, and a pattern designing method thereof, more particularly, relates to an electron beam exposure mask for preventing deformation of a stencil mask and a pattern designing method thereof.
2. Description of the Related Art
In a process of manufacturing a semiconductor integrated circuit device, there has been practically used a fine processing technology for drawing an integrated circuit pattern by drawing electron beams (EB) and using a focused beam of charged particles. For example, in an electron beam exposure system, electron beams are emitted to a wafer on which an electron beam sensitive resist is applied, whereby an integrated circuit pattern is directed exposed to the electron beam sensitive resist. An EB mask is used in order to obtain a drawing pattern caused by electron beams. Such techniques for drawing electron beams using such electron beams include a character projection technique of projecting a mask pattern in a reduced size to image a unit region such as a memory cell in batch. In addition, a mask used for character projection to emit a circuit pattern onto a wafer in batch includes a stencil mask having a hole for electron beams to pass, the stencil mask transferring a circuit pattern.
In the stencil mask, however, in a region whose periphery is surrounded by a mask hole, any portion for supporting this region does not exist, and thus, a stencil mask having such a pattern cannot be fabricated. Such a problem is generally called a xe2x80x9cdoughnutxe2x80x9d problem.
Conventionally, two masks are used for a mask pattern having such a doughnut problem, thereby fabricating a stencil mask. FIG. 1A is a plan view showing a designed mask pattern having the doughnut problem. FIG. 1B is a plan view showing an example of a complementary mask relevant to the mask pattern shown in FIG. 1A. FIG. 1C is a plan view showing another example of the complementary mask.
For example, in the case where a mask pattern 20 consisting of a doughnut pattern 20a and a line pattern opening 20b provided therein is designed, as shown in FIG. 1A, there are used a first complementary mask 21 on which there are formed a mask hole 23a that is half of the doughnut pattern 20a and a mask hole 23b of a line pattern opening 20b, and a second complementary mask 22 having a mask hole 23c that is the residue of the doughnut pattern 20a, as shown in FIG. 1B. As shown in FIG. 1C, there may be used a first complementary mask 21 on which there are formed a mask hole 23d that correspond to one side of the doughnut pattern 20a and a mask hole 23b of a line pattern opening 20b, and a second complementary mask 22 on which there is formed a mask hole 23e that corresponds to the remaining three sides of the doughnut pattern 20a.
In this way, an inside region of the doughnut pattern 21a is supported by using two complementary masks 21 and 22, and a line pattern designed in that region can be left.
However, although the above mentioned complementary masks 21 and 22 are used, whereby a stencil mask can be fabricated while avoiding the doughnut problem, there is a problem that a deformation such as warping occurs in the fabricated stencil mask. Namely, for example, in the second complementary mask 22 shown in FIG. 1B, a region extending like a tongue is supported with a point on a line segment connecting ends of the mask hole 23c being a fulcrum. However, in the case where strength in the boundary region is low, a deformation such as warping may occur in a region that extends like a tongue. Further, in the case where a deformation is significant, a breakage may occur. Such a deformation becomes significant in the second complementary mask shown in FIG. 1C. In addition, the above deformation may occur similarly in the first complementary mask 21 shown in FIG. 1B as well. Such a problem may be called a xe2x80x9ctonguexe2x80x9d problem. In addition, in the case where mask pattern ends are proximal to each other, and a portion for supporting a portion that extends like a tongue is very small, the above-described deformation occurs significantly. Such a problem may be called a xe2x80x9cleafxe2x80x9d problem.
In addition, in a line and space (L/S) pattern such as a bit line and a word line for a memory as well, there is a problem that a stencil mask is deformed. FIG. 2A is a plan view showing a stencil mask immediately after a mask hole has been formed. FIG. 2B is a plan view showing a stencil mask after a washing process after the mask hole has been formed.
As shown in FIG. 2B, in a stencil mask for an L/S pattern 24, in a washing process performed after the mask hole 25 has been formed, there is a problem that adjacent line portions come into contact with each other due to surface tension of pure water or the like, and cannot be separated by a force between molecules.
Such a problem that the line portions come into contact with each other exists in a variety of patterns if a deformation is greater than a predetermined extent. Considering the fact that a complicated mask pattern increases, it is very difficult to fabricate the stencil mask at a present stage. FIG. 3 is a plan view showing an example of a comparatively complicated stencil mask.
It is an object of the present invention to provide an electron beam exposure mask hardly deformed by a washing process or the like after a mask hole has been formed, the electron beam exposure mask being capable of performing exposure with high dimensional precision and a pattern designing method thereof.
According to one aspect of the present invention, an electron beam exposure mask comprises a mask body being defined to a plurality of lattice shaped regions with a uniform dimension. An opening through which electron beams pass is provided at only one of two lattice shaped regions which are adjacent to each other among the plurality of lattice shaped regions. Lattice shaped regions in which the opening may be provided configure a checkerboard pattern.
According to another aspect of the present invention, an electron beam exposure mask comprising a mask body being defined to a plurality of first lattice shaped regions with a first uniform dimension. First openings through which electron beams pass are provided at any of first lattice shaped regions which are not adjacent to each other among the plurality of first lattice shaped regions. First lattice shaped regions in which the first opening does not exist are defined to a plurality of second lattice shaped regions with a second uniform dimension smaller than the first uniform dimension. Second openings through which electron beam pass are provided at only one of two second lattice shaped regions which are adjacent to each other among the plurality of second lattice shaped regions.
Conventionally a complementary mask pattern is determined in order to avoid the doughnut problem. In contrast, in the present invention, an opening exists only in one of the lattice shaped regions that are adjacent to each other or no opening exists in a lattice shaped region in which first and second openings do not exist. Therefore, a portion at which a deformation is locally significant does not exist, and, for example, a mask deformation is unlikely to occur in a washing process using pure water as well. As a result, the yield of an electron exposure mask increases, and its dimensional precision is improved.
In addition, in a line and space shaped pattern, if the shape of an opening is determined so that a displacement caused by a stress acting to each location is less than a predetermined value, its dimensional precision is improved and its dimensional precision is also improved.
According to the present invention, the shape of an opening is determined so that a displacement after the opening has been formed is less than a predetermined value. Thus, for example, in the washing processing using pure water, holder attachment process, and an electron beam exposure process in which a temperature rise occurs or the like as well, a mask deformation can be restrained. Thus, the yield of an electron beam exposure mask can be improved, and its dimensional precision can be improved.
In addition, if a lattice shaped region is assigned so as to configure a checkerboard pattern, a complicated algorithm is eliminated, and very simple design can be made. Further, the pattern density between complementary masks becomes almost uniform, beam blurring due to the Coulomb effect becomes uniform, and the precision of an exposed pattern can be improved.